1. Field of the Invention
The present invention relates to a phase-shift blankmask and a method of fabricating the same, and more particularly, to a phase-shift blankmask including a phase-shift layer having improved chemical resistance and durability to have a thin thickness suitable for a semiconductor manufacturing process using KrF and ArF excimer lasers and a method of fabricating the same.
2. Discussion of Related Art
Today, as a need for a fine circuit pattern has been accompanied by high integration of large-scale integrated circuits (ICs), high semiconductor microfabrication process technology has emerged as a very important issue. In the case of a highly integrated circuit, circuit wires become finer for low power consumption and high-speed operations, and there is a growing technical need for a contact hole pattern for an interlayer connection and a circuit arrangement for high integration. Thus, in order to satisfy such demands, technology for a photomask on which an original circuit pattern is recorded needs to be manufactured to be finer and to be capable of recording a more precise circuit pattern thereon.
A photolithography technology has been developed to shorten an exposure wavelength by using a 436 nm g-line, a 365 nm i-line, 248 nm KrF laser, or 193 nm ArF laser in order to improve the resolution of a semiconductor circuit pattern. However, the shortening of the exposure wavelength greatly contributes to an improvement in the resolution of a semiconductor circuit pattern but deteriorates a depth of focus (DoF), thereby increasing a burden on design of an optical system including a lens.
Accordingly, in order to solve this problem, a phase-shift mask has been developed to improve both the resolution and DoF of a semiconductor circuit pattern using a phase-shift layer that shifts the phase of exposure light by 180 degrees. A phase-shift blankmask has a structure in which a phase-shift layer, a light-shielding film, and a photoresist film are stacked on a transparent substrate. The phase-shift blankmask can be used as a blankmask for realizing a high-precision minimum critical dimension (CD) of 90 nm or less during a semiconductor photolithography process, and particularly, can be used in the field of lithography using 248 nm KrF laser or 193 nm ArF laser and the field of immersion exposure lithography.
During a process of cleaning a photomask formed as a phase-shift blankmask, a cleaning solution containing an acid material, such as sulfuric acid, and a basic material, such as ammonium, have been used but a cleaning process using hot deionized water and ozone (O3) water has recently been introduced. However, a conventional phase-shift layer, e.g., a phase-shift layer having nitrogen (N)-containing metal silicide, has a certain degree of chemical resistance to acid and basic chemicals but has low durability with respect to hot deionized water and ozone water. Also, a phase-shift layer having nitrogen (N) and oxygen (O)-containing metal silicide has low durability with respect to a cleaning solution containing acid and basic materials. Thus, phase-shift layers become thicker and thicker to compensate for variations in a refractive index and phase shift degree thereof.
As a cleaning process is repeatedly performed during manufacture of a photomask and during use of the photomask, a thickness of a phase-shift layer changes, thus causing a change in the optical characteristics (e.g., a degree of phase shift, transmissivity, reflectivity, etc.) of the photomask. Furthermore, as the cleaning process is repeatedly performed, surfaces of the phase-shift layer are damaged to cause a change in surface roughness and flatness thereof. Accordingly, the durability of the phase-shift layer is degraded, and it is thus difficult to manufacture a reliable photomask.